[clang] [clang] Catch missing format attributes (PR #105479)

Budimir Aranđelović via cfe-commits cfe-commits at lists.llvm.org
Tue Sep 3 01:47:57 PDT 2024


https://github.com/budimirarandjelovichtec updated https://github.com/llvm/llvm-project/pull/105479

>From 5604c2f5d11a340413f638f275e5c91da76fe6d9 Mon Sep 17 00:00:00 2001
From: budimirarandjelovicsyrmia <budimir.arandjelovic at syrmia.com>
Date: Fri, 5 Apr 2024 15:20:37 +0200
Subject: [PATCH] [clang] Catch missing format attributes

---
 clang/docs/ReleaseNotes.rst                   |   3 +
 clang/include/clang/Basic/DiagnosticGroups.td |   1 -
 .../clang/Basic/DiagnosticSemaKinds.td        |   3 +
 clang/include/clang/Sema/Attr.h               |   7 +
 clang/include/clang/Sema/Sema.h               |   2 +
 clang/lib/Sema/SemaDecl.cpp                   |   2 +
 clang/lib/Sema/SemaDeclAttr.cpp               | 210 ++++++++++++++-
 clang/test/Sema/attr-format-missing.c         | 251 ++++++++++++++++++
 clang/test/Sema/attr-format-missing.cpp       | 176 ++++++++++++
 9 files changed, 652 insertions(+), 3 deletions(-)
 create mode 100644 clang/test/Sema/attr-format-missing.c
 create mode 100644 clang/test/Sema/attr-format-missing.cpp

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 49c4b0c601159b..daf78d8981b2de 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -268,6 +268,9 @@ Improvements to Clang's diagnostics
 
 - Improved diagnostic when trying to overload a function in an ``extern "C"`` context. (#GH80235)
 
+- Clang now diagnoses missing format attributes for non-template functions and
+  class/struct/union members. Fixes #GH60718
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index c4c29942ee1cbd..9defe82ef7023d 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -529,7 +529,6 @@ def MainReturnType : DiagGroup<"main-return-type">;
 def MaxUnsignedZero : DiagGroup<"max-unsigned-zero">;
 def MissingBraces : DiagGroup<"missing-braces">;
 def MissingDeclarations: DiagGroup<"missing-declarations">;
-def : DiagGroup<"missing-format-attribute">;
 def MissingIncludeDirs : DiagGroup<"missing-include-dirs">;
 def MissingNoreturn : DiagGroup<"missing-noreturn">;
 def MultiChar : DiagGroup<"multichar">;
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index dcb49d8a67604a..d1facae96e8ddb 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1040,6 +1040,9 @@ def err_opencl_invalid_param : Error<
 def err_opencl_invalid_return : Error<
   "declaring function return value of type %0 is not allowed %select{; did you forget * ?|}1">;
 def warn_enum_value_overflow : Warning<"overflow in enumeration value">;
+def warn_missing_format_attribute : Warning<
+  "diagnostic behavior may be improved by adding the %0 format attribute to the declaration of %1">,
+  InGroup<DiagGroup<"missing-format-attribute">>, DefaultIgnore;
 def warn_pragma_options_align_reset_failed : Warning<
   "#pragma options align=reset failed: %0">,
   InGroup<IgnoredPragmas>;
diff --git a/clang/include/clang/Sema/Attr.h b/clang/include/clang/Sema/Attr.h
index 3f0b10212789a4..37c124ca7b454a 100644
--- a/clang/include/clang/Sema/Attr.h
+++ b/clang/include/clang/Sema/Attr.h
@@ -123,6 +123,13 @@ inline bool isInstanceMethod(const Decl *D) {
   return false;
 }
 
+inline bool checkIfMethodHasImplicitObjectParameter(const Decl *D) {
+  if (const auto *MethodDecl = dyn_cast<CXXMethodDecl>(D))
+    return MethodDecl->isInstance() &&
+           !MethodDecl->hasCXXExplicitFunctionObjectParameter();
+  return false;
+}
+
 /// Diagnose mutually exclusive attributes when present on a given
 /// declaration. Returns true if diagnosed.
 template <typename AttrTy>
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 0358259945c796..b128d911d27294 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -4640,6 +4640,8 @@ class Sema final : public SemaBase {
 
   enum class RetainOwnershipKind { NS, CF, OS };
 
+  void DiagnoseMissingFormatAttributes(Stmt *Body, const FunctionDecl *FDecl);
+
   UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,
                           StringRef UuidAsWritten, MSGuidDecl *GuidDecl);
 
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 0f63c764536ecb..34ff1289bf06e8 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16007,6 +16007,8 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
         }
       }
 
+      DiagnoseMissingFormatAttributes(Body, FD);
+
       // We might not have found a prototype because we didn't wish to warn on
       // the lack of a missing prototype. Try again without the checks for
       // whether we want to warn on the missing prototype.
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 33547c2e6e1452..2e877d1fa6b83c 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -3519,7 +3519,7 @@ static void handleFormatAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
 
   // In C++ the implicit 'this' function parameter also counts, and they are
   // counted from one.
-  bool HasImplicitThisParam = isInstanceMethod(D);
+  bool HasImplicitThisParam = checkIfMethodHasImplicitObjectParameter(D);
   unsigned NumArgs = getFunctionOrMethodNumParams(D) + HasImplicitThisParam;
 
   IdentifierInfo *II = AL.getArgAsIdent(0)->Ident;
@@ -3632,7 +3632,7 @@ static void handleCallbackAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
     return;
   }
 
-  bool HasImplicitThisParam = isInstanceMethod(D);
+  bool HasImplicitThisParam = checkIfMethodHasImplicitObjectParameter(D);
   int32_t NumArgs = getFunctionOrMethodNumParams(D);
 
   FunctionDecl *FD = D->getAsFunction();
@@ -5335,6 +5335,212 @@ static void handlePreferredTypeAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
   D->addAttr(::new (S.Context) PreferredTypeAttr(S.Context, AL, ParmTSI));
 }
 
+// Returns vector of format attributes. There are no two attributes with same
+// arguments in returning vector. There can be attributes that effectively only
+// store information about format type.
+static std::vector<FormatAttr *>
+GetMissingFormatAttributes(Sema &S, Stmt *Body, const FunctionDecl *FDecl) {
+  unsigned int FunctionFormatArgumentIndexOffset =
+      checkIfMethodHasImplicitObjectParameter(FDecl) ? 2 : 1;
+
+  std::vector<FormatAttr *> MissingAttributes;
+
+  // Iterate over body statements.
+  for (auto *Child : Body->children()) {
+    // If child statement is compound statement, recursively get missing
+    // attributes.
+    if (dyn_cast_or_null<CompoundStmt>(Child)) {
+      std::vector<FormatAttr *> CompoundStmtMissingAttributes =
+          GetMissingFormatAttributes(S, Child, FDecl);
+
+      // If there are already missing attributes with same arguments, do not add
+      // duplicates.
+      for (FormatAttr *FA : CompoundStmtMissingAttributes) {
+        if (!llvm::any_of(MissingAttributes, [&](const FormatAttr *Attr) {
+              return FA->getType() == Attr->getType() &&
+                     FA->getFormatIdx() == Attr->getFormatIdx() &&
+                     FA->getFirstArg() == Attr->getFirstArg();
+            }))
+          MissingAttributes.push_back(FA);
+      }
+
+      continue;
+    }
+
+    ValueStmt *VS = dyn_cast_or_null<ValueStmt>(Child);
+    if (!VS)
+      continue;
+    Expr *TheExpr = VS->getExprStmt();
+    if (!TheExpr)
+      continue;
+    CallExpr *TheCall = dyn_cast_or_null<CallExpr>(TheExpr);
+    if (!TheCall)
+      continue;
+    const FunctionDecl *CalleeFunction =
+        dyn_cast_or_null<FunctionDecl>(TheCall->getCalleeDecl());
+    if (!CalleeFunction || !CalleeFunction->hasAttr<FormatAttr>())
+      continue;
+
+    Expr **Args = TheCall->getArgs();
+    unsigned int NumArgs = TheCall->getNumArgs();
+
+    // If callee expression is function, check if it is format function.
+    // If it is, check if caller function misses format attributes.
+
+    unsigned int CalleeFunctionFormatArgumentIndexOffset =
+        checkIfMethodHasImplicitObjectParameter(CalleeFunction) ? 2 : 1;
+
+    // If callee function is format function and format arguments are not
+    // relevant to emit diagnostic, save only information about format type
+    // (format index and first-to-check argument index are set to -1).
+    // Information about format type is later used to determine if there are
+    // more than one format type found.
+
+    // Check if function has format attribute with forwarded format string.
+    IdentifierInfo *AttrType;
+    const ParmVarDecl *FormatArg;
+    if (!llvm::any_of(CalleeFunction->specific_attrs<FormatAttr>(),
+                      [&](const FormatAttr *Attr) {
+                        AttrType = Attr->getType();
+
+                        int OffsetFormatIndex =
+                            Attr->getFormatIdx() -
+                            CalleeFunctionFormatArgumentIndexOffset;
+                        if (OffsetFormatIndex < 0 ||
+                            (unsigned)OffsetFormatIndex >= NumArgs)
+                          return false;
+
+                        if (const auto *FormatArgExpr = dyn_cast<DeclRefExpr>(
+                                Args[OffsetFormatIndex]->IgnoreParenCasts()))
+                          if (FormatArg = dyn_cast_or_null<ParmVarDecl>(
+                                  FormatArgExpr->getReferencedDeclOfCallee()))
+                            return true;
+                        return false;
+                      })) {
+      MissingAttributes.push_back(
+          FormatAttr::CreateImplicit(S.getASTContext(), AttrType, -1, -1));
+      continue;
+    }
+
+    // Do not add in a vector format attributes whose type is different than
+    // caller function attribute type.
+    if (llvm::any_of(FDecl->specific_attrs<FormatAttr>(),
+                     [AttrType](const FormatAttr *FunctionAttr) {
+                       return AttrType != FunctionAttr->getType();
+                     }))
+      continue;
+
+    // Check if format string argument is caller function parameter.
+    int StringIndex = 0;
+    if (!llvm::any_of(FDecl->parameters(), [&](const ParmVarDecl *Param) {
+          if (Param != FormatArg)
+            return false;
+
+          StringIndex = Param->getFunctionScopeIndex() +
+                        FunctionFormatArgumentIndexOffset;
+
+          return true;
+        })) {
+      MissingAttributes.push_back(
+          FormatAttr::CreateImplicit(S.getASTContext(), AttrType, -1, -1));
+      continue;
+    }
+
+    unsigned NumOfParentFunctionParams = FDecl->getNumParams();
+
+    // Compare caller and callee function format attribute arguments (archetype
+    // and format string).
+    if (llvm::any_of(
+            FDecl->specific_attrs<FormatAttr>(), [&](const FormatAttr *Attr) {
+              if (Attr->getType() != AttrType)
+                return false;
+              int OffsetFormatIndex =
+                  Attr->getFormatIdx() - FunctionFormatArgumentIndexOffset;
+
+              if (OffsetFormatIndex < 0 ||
+                  (unsigned)OffsetFormatIndex >= NumOfParentFunctionParams)
+                return false;
+
+              if (FDecl->parameters()[OffsetFormatIndex] != FormatArg)
+                return false;
+
+              return true;
+            })) {
+      MissingAttributes.push_back(
+          FormatAttr::CreateImplicit(S.getASTContext(), AttrType, -1, -1));
+      continue;
+    }
+
+    // Get first argument index
+    int FirstToCheck = [&]() -> unsigned {
+      if (!FDecl->isVariadic())
+        return 0;
+      const auto *FirstToCheckArg = Args[NumArgs - 1]->IgnoreParenCasts();
+      if (FirstToCheckArg->getType().getCanonicalType() !=
+          S.getASTContext().getBuiltinVaListType().getCanonicalType())
+        return 0;
+      return NumOfParentFunctionParams + FunctionFormatArgumentIndexOffset;
+    }();
+
+    // If there are already attributes which arguments matches arguments
+    // detected in this iteration, do not add new attribute as it would be
+    // duplicate.
+    if (!llvm::any_of(MissingAttributes, [&](const FormatAttr *Attr) {
+          return Attr->getType() == AttrType &&
+                 Attr->getFormatIdx() == StringIndex &&
+                 Attr->getFirstArg() == FirstToCheck;
+        }))
+      MissingAttributes.push_back(FormatAttr::CreateImplicit(
+          S.getASTContext(), AttrType, StringIndex, FirstToCheck));
+  }
+
+  return MissingAttributes;
+}
+
+// This function is called only if function call is not inside template body.
+// TODO: Add call for function calls inside template body.
+// Emit warnings if caller function misses format attributes.
+void Sema::DiagnoseMissingFormatAttributes(Stmt *Body,
+                                           const FunctionDecl *FDecl) {
+  assert(FDecl);
+
+  // If there are no function body, exit.
+  if (!Body)
+    return;
+
+  // Get missing format attributes
+  std::vector<FormatAttr *> MissingFormatAttributes =
+      GetMissingFormatAttributes(*this, Body, FDecl);
+  if (MissingFormatAttributes.empty())
+    return;
+
+  // Check if there are more than one format type found. In that case do not
+  // emit diagnostic.
+  const clang::IdentifierInfo *AttrType = MissingFormatAttributes[0]->getType();
+  if (llvm::any_of(MissingFormatAttributes, [&](const FormatAttr *Attr) {
+        return AttrType != Attr->getType();
+      }))
+    return;
+
+  for (const FormatAttr *FA : MissingFormatAttributes) {
+    // If format index and first-to-check argument index are negative, it means
+    // that this attribute is only saved for multiple format types checking.
+    if (FA->getFormatIdx() < 0 || FA->getFirstArg() < 0)
+      continue;
+
+    // Emit diagnostic
+    SourceLocation Loc = FDecl->getLocation();
+    Diag(Loc, diag::warn_missing_format_attribute)
+        << FA->getType() << FDecl
+        << FixItHint::CreateInsertion(Loc,
+                                      (llvm::Twine("__attribute__((format(") +
+                                       FA->getType()->getName() + ", " +
+                                       llvm::Twine(FA->getFormatIdx()) + ", " +
+                                       llvm::Twine(FA->getFirstArg()) + ")))")
+                                          .str());
+  }
+}
+
 //===----------------------------------------------------------------------===//
 // Microsoft specific attribute handlers.
 //===----------------------------------------------------------------------===//
diff --git a/clang/test/Sema/attr-format-missing.c b/clang/test/Sema/attr-format-missing.c
new file mode 100644
index 00000000000000..339fdee08bfa27
--- /dev/null
+++ b/clang/test/Sema/attr-format-missing.c
@@ -0,0 +1,251 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,c_diagnostics -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -Wmissing-format-attribute -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -verify=expected,cpp_diagnostics -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -verify=expected,cpp_diagnostics -std=c++2b -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -verify=expected,cpp_diagnostics -std=c++23 -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -x c++ -Wmissing-format-attribute -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+
+#ifndef __cplusplus
+typedef __CHAR16_TYPE__ char16_t;
+typedef __CHAR32_TYPE__ char32_t;
+typedef __WCHAR_TYPE__ wchar_t;
+#endif
+
+typedef __SIZE_TYPE__ size_t;
+typedef __builtin_va_list va_list;
+
+__attribute__((__format__(__printf__, 1, 2)))
+int printf(const char *, ...); // #printf
+
+__attribute__((__format__(__scanf__, 1, 2)))
+int scanf(const char *, ...); // #scanf
+
+__attribute__((__format__(__printf__, 1, 0)))
+int vprintf(const char *, va_list); // #vprintf
+
+__attribute__((__format__(__scanf__, 1, 0)))
+int vscanf(const char *, va_list); // #vscanf
+
+__attribute__((__format__(__printf__, 2, 0)))
+int vsprintf(char *, const char *, va_list); // #vsprintf
+
+__attribute__((__format__(__printf__, 3, 0)))
+int vsnprintf(char *ch, size_t, const char *, va_list); // #vsnprintf
+
+#ifndef __cplusplus
+int vwscanf(const wchar_t *, va_list); // #vwscanf
+#endif
+
+__attribute__((__format__(__scanf__, 1, 4)))
+void f1(char *out, const size_t len, const char *format, ... /* args */) // #f1
+{
+    va_list args;
+    vsnprintf(out, len, format, args); // expected-no-warning@#f1
+}
+
+__attribute__((__format__(__printf__, 1, 4)))
+void f2(char *out, const size_t len, const char *format, ... /* args */) // #f2
+{
+    va_list args;
+    vsnprintf(out, len, format, args); // expected-warning@#f2 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f2'}}
+                                       // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(printf, 3, 4)))"
+}
+
+void f3(char *out, va_list args) // #f3
+{
+    vprintf(out, args); // expected-warning@#f3 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f3'}}
+                        // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:6-[[@LINE-3]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+void f4(char* out, ... /* args */) // #f4
+{
+    va_list args;
+    vprintf("test", args); // expected-no-warning@#f4
+
+    const char *ch;
+    vprintf(ch, args); // expected-no-warning@#f4
+}
+
+void f5(va_list args) // #f5
+{
+    char *ch;
+    vscanf(ch, args); // expected-no-warning@#f5
+}
+
+void f6(char *out, va_list args) // #f6
+{
+    char *ch;
+    vprintf(ch, args); // expected-no-warning@#f6
+    vprintf("test", args); // expected-no-warning@#f6
+    vprintf(out, args); // expected-warning@#f6 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f6'}}
+                        // CHECK: fix-it:"{{.*}}":{[[@LINE-6]]:6-[[@LINE-6]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+void f7(const char *out, ... /* args */) // #f7
+{
+    va_list args;
+
+    vscanf(out, args); // expected-warning@#f7 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'f7'}}
+                       // CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:6-[[@LINE-5]]:6}:"__attribute__((format(scanf, 1, 2)))"
+}
+
+void f8(const char *out, ... /* args */) // #f8
+{
+    va_list args;
+
+    vscanf(out, args); // expected-no-warning@#f8
+    vprintf(out, args); // expected-no-warning@#f8
+}
+
+void f9(const char out[], ... /* args */) // #f9
+{
+    va_list args;
+    char *ch;
+    vprintf(ch, args); // expected-no-warning
+    vsprintf(ch, out, args); // expected-warning@#f9 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f9'}}
+                             // CHECK: fix-it:"{{.*}}":{[[@LINE-6]]:6-[[@LINE-6]]:6}:"__attribute__((format(printf, 1, 2)))"
+}
+
+#ifndef __cplusplus
+void f10(const wchar_t *out, ... /* args */) // #f10
+{
+    va_list args;
+    vwscanf(out, args); // expected-no-warning@#f10
+}
+#endif
+
+void f11(const char *out) // #f11
+{
+    va_list args;
+    vscanf(out, args); // expected-warning@#f11 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'f11'}}
+                       // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(scanf, 1, 0)))"
+}
+
+void f12(char* out) // #f12
+{
+    va_list args;
+    const char* ch;
+    vsprintf(out, ch, args); // expected-no-warning@#f12
+    vprintf(out, args); // expected-warning@#f12 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f12'}}
+                        // CHECK: fix-it:"{{.*}}":{[[@LINE-6]]:6-[[@LINE-6]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+void f13(const char *out, ... /* args */) // #f13
+{
+    int a;
+    printf(out, a); // expected-warning@#f13 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f13'}}
+                    // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+void f14(const char *out, ... /* args */) // #f14
+{
+    printf(out, 1); // expected-warning@#f14 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f14'}}
+                    // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:6-[[@LINE-3]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+__attribute__((format(printf, 1, 2)))
+void f15(const char *out, ... /* args */) // #f15
+{
+    int a;
+    printf(out, a); // expected-no-warning@#f15
+}
+
+__attribute__((format(printf, 1, 2)))
+void f16(const char *out, ... /* args */) // #f16
+{
+    printf(out, 1); // expected-no-warning@#f16
+}
+
+__attribute__((format(printf, 1, 2)))
+void f17(const char *out, ... /* args */) // #f17
+{
+    int a;
+    printf(out, a); // expected-no-warning@#f17
+    printf(out, 1); // expected-no-warning@#f17
+}
+
+void f18(char *out, ... /* args */) // #f18
+{
+    va_list args;
+    scanf(out, args); // expected-no-warning@#f18
+    {
+        printf(out, args); // expected-no-warning@#f18
+    }
+}
+
+void f19(char *out, va_list args) // #f19
+{
+    {
+        scanf(out, args); // expected-no-warning@#f19
+        printf(out, args); // expected-no-warning@#f19
+    }
+}
+
+// expected-warning@#f20 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'f20'}}
+// CHECK: fix-it:"{{.*}}":{[[@LINE+1]]:6-[[@LINE+1]]:6}:"__attribute__((format(scanf, 1, 2)))"
+void f20(char *out, ... /* args */) // #f20
+{
+    va_list args;
+    scanf(out, args);
+    {
+        scanf(out, args);
+    }
+}
+
+void f21(char* ch, const char *out, ... /* args */) // #f21
+{
+    va_list args;
+    printf(ch, args); // expected-warning@#f21 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f21}}
+                      // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(printf, 1, 3)))"
+    int a;
+    printf(out, a); // expected-warning@#f21 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f21'}}
+                    // CHECK: fix-it:"{{.*}}":{[[@LINE-7]]:6-[[@LINE-7]]:6}:"__attribute__((format(printf, 2, 0)))"
+    printf(out, 1); // no warning because first command above emitted same warning and fix-it
+    printf(out, args); // expected-warning@#f21 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f21'}}
+                       // CHECK: fix-it:"{{.*}}":{[[@LINE-10]]:6-[[@LINE-10]]:6}:"__attribute__((format(printf, 2, 3)))"
+}
+
+typedef va_list tdVaList;
+typedef int tdInt;
+
+void f22(const char *out, ... /* args */) // #f22
+{
+    tdVaList args;
+    printf(out, args); // expected-warning@#f22 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f22'}}
+                       // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(printf, 1, 2)))"
+}
+
+void f23(const char *out, ... /* args */) // #f23
+{
+    tdInt a;
+    scanf(out, a); // expected-warning@#f23 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'f23'}}
+                   // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(scanf, 1, 0)))"
+}
+
+void f24(const char *out, tdVaList args) // #f24
+{
+    scanf(out, args); // expected-warning@#f24 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'f24'}}
+                      // CHECK: fix-it:"{{.*}}":{[[@LINE-3]]:6-[[@LINE-3]]:6}:"__attribute__((format(scanf, 1, 0)))"
+}
+
+void f25(const char *out, tdVaList args) // #f25
+{
+    tdInt a;
+    printf(out, a); // expected-warning@#f25 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'f25'}}
+                    // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:6-[[@LINE-4]]:6}:"__attribute__((format(printf, 1, 0)))"
+}
+
+void f26(char *out, ... /* args */) // #f26
+{
+    va_list args;
+    char *ch;
+    vscanf(ch, args); // expected-no-warning@#f26
+    vprintf(out, args); // expected-no-warning@#f26
+}
+
+void f27(char *out, ... /* args */) // #f27
+{
+    va_list args;
+    vscanf("%s", args); // expected-no-warning@#f27
+    vprintf(out, args); // expected-no-warning@#f27
+}
diff --git a/clang/test/Sema/attr-format-missing.cpp b/clang/test/Sema/attr-format-missing.cpp
new file mode 100644
index 00000000000000..5ee2a679f84168
--- /dev/null
+++ b/clang/test/Sema/attr-format-missing.cpp
@@ -0,0 +1,176 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=expected,beforeCxx2b -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++2b -Wmissing-format-attribute %s
+// RUN: %clang_cc1 -fsyntax-only -verify -std=c++23 -Wmissing-format-attribute %s
+// RUN: not %clang_cc1 -fsyntax-only -Wmissing-format-attribute -fdiagnostics-parseable-fixits %s 2>&1 | FileCheck %s
+
+typedef __SIZE_TYPE__ size_t;
+typedef __builtin_va_list va_list;
+
+namespace std
+{
+    template<class Elem> struct basic_string_view {};
+    template<class Elem> struct basic_string {
+        const Elem *c_str() const noexcept;
+        basic_string(const basic_string_view<Elem> SW);
+    };
+
+    using string = basic_string<char>;
+    using wstring = basic_string<wchar_t>;
+    using string_view = basic_string_view<char>;
+    using wstring_view = basic_string_view<wchar_t>;
+}
+
+__attribute__((__format__(__printf__, 1, 2)))
+int printf(const char *, ...); // #printf
+
+__attribute__((__format__(__scanf__, 1, 2)))
+int scanf(const char *, ...); // #scanf
+
+__attribute__((__format__(__printf__, 1, 0)))
+int vprintf(const char *, va_list); // #vprintf
+
+__attribute__((__format__(__scanf__, 1, 0)))
+int vscanf(const char *, va_list); // #vscanf
+
+__attribute__((__format__(__printf__, 2, 0)))
+int vsprintf(char *, const char *, va_list); // #vsprintf
+
+__attribute__((__format__(__printf__, 3, 0)))
+int vsnprintf(char *, size_t, const char *, va_list); // #vsnprintf
+
+int vwprintf(const wchar_t *, va_list); // #vwprintf
+
+void f1(const std::string &str, ... /* args */) // #f1
+{
+    va_list args;
+    vscanf(str.c_str(), args); // expected-no-warning@#f1
+}
+
+__attribute__((format(printf, 1, 2))) // expected-error {{format argument not a string type}}
+void f2(const std::string &str, ... /* args */); // #f2
+
+void f3(std::string_view str, ... /* args */) // #f3
+{
+    va_list args;
+    vscanf(std::string(str).c_str(), args); // expected-no-warning@#f3
+}
+
+__attribute__((format(printf, 1, 2))) // expected-error {{format argument not a string type}}
+void f4(std::string_view str, ... /* args */); // #f4
+
+void f5(const std::wstring &str, ... /* args */) // #f5
+{
+    va_list args;
+    vwprintf(str.c_str(), args); // expected-no-warning@#f5
+}
+
+__attribute__((format(printf, 1, 2))) // expected-error {{format argument not a string type}}
+void f6(const std::wstring &str, ... /* args */); // #f6
+
+void f7(std::wstring_view str, ... /* args */) // #f7
+{
+    va_list args;
+    vwprintf(std::wstring(str).c_str(), args); // expected-no-warning@#f7
+}
+
+__attribute__((format(printf, 1, 2))) // expected-error {{format argument not a string type}}
+void f8(std::wstring_view str, ... /* args */); // #f8
+
+struct S1
+{
+    void fn1(const char *out, ... /* args */) // #S1_fn1
+    {
+        va_list args;
+        vscanf(out, args); // expected-warning@#S1_fn1 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'fn1'}}
+                           // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(scanf, 2, 3)))"
+    }
+
+    __attribute__((format(scanf, 2, 0)))
+    void fn2(const char *out, va_list args); // #S1_fn2
+
+    void fn3(const char *out, ... /* args */);
+
+    void fn4(this S1& expliciteThis, const char *out, va_list args) // #S1_fn4
+    {
+        expliciteThis.fn2(out, args); // beforeCxx2b-error@#S1_fn4 {{explicit object parameters are incompatible with C++ standards before C++2b}}
+                                      // expected-warning@#S1_fn4 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'fn4'}}
+                                      // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(scanf, 2, 0)))"
+    }
+};
+
+void S1::fn3(const char *out, ... /* args */) // #S1_fn3
+{
+    va_list args;
+    fn2(out, args); // expected-warning@#S1_fn3 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'fn3'}}
+                    // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(scanf, 2, 3)))"
+}
+
+union U1
+{
+    __attribute__((format(printf, 2, 0)))
+    void fn1(const char *out, va_list args); // #U1_fn1
+
+    void fn2(const char *out, ... /* args */) // #U1_fn2
+    {
+        va_list args;
+        fn1(out, args); // expected-warning@#U1_fn2 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'fn2'}}
+                        // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(printf, 2, 3)))"
+    }
+
+    void fn3(this U1&, const char *out) // #U1_fn3
+    {
+        va_list args;
+        printf(out, args); // beforeCxx2b-error@#U1_fn3 {{explicit object parameters are incompatible with C++ standards before C++2b}}
+                           // expected-warning@#U1_fn3 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'fn3'}}
+                           // CHECK: fix-it:"{{.*}}":{[[@LINE-5]]:10-[[@LINE-5]]:10}:"__attribute__((format(printf, 2, 0)))"
+    }
+};
+
+class C1
+{
+    __attribute__((format(printf, 3, 0)))
+    void fn1(const int n, const char *out, va_list args); // #C1_fn1
+
+    void fn2(const char *out, const int n, ... /* args */) // #C1_fn2
+    {
+        va_list args;
+        fn1(n, out, args); // expected-warning@#C1_fn2 {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'fn2'}}
+                           // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(printf, 2, 4)))"
+    }
+
+    void fn3(this const C1&, const char *out, va_list args) // #C1_fn3
+    {
+        scanf(out, args); // beforeCxx2b-error@#C1_fn3 {{explicit object parameters are incompatible with C++ standards before C++2b}}
+                          // expected-warning@#C1_fn3 {{diagnostic behavior may be improved by adding the 'scanf' format attribute to the declaration of 'fn3'}}
+                          // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:10-[[@LINE-4]]:10}:"__attribute__((format(scanf, 2, 0)))"
+    }
+
+    C1(const int n, const char *out) //#C1_C1a
+    {
+        va_list args;
+        fn1(n, out, args); // expected-warning@#C1_C1a {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'C1'}}
+                           // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:5-[[@LINE-4]]:5}:"__attribute__((format(printf, 3, 0)))"
+    }
+
+    C1(const char *out, ... /* args */) // #C1_C1b
+    {
+        va_list args;
+        printf(out, args); // expected-warning@#C1_C1b {{diagnostic behavior may be improved by adding the 'printf' format attribute to the declaration of 'C1'}}
+                           // CHECK: fix-it:"{{.*}}":{[[@LINE-4]]:5-[[@LINE-4]]:5}:"__attribute__((format(printf, 2, 3)))"
+    }
+
+    ~C1() // #d_C1
+    {
+        const char *out;
+        va_list args;
+        vprintf(out, args); // expected-no-warning@#d_C1
+    }
+};
+
+// TODO: implement for templates
+template <int N>
+void func(char (&str)[N], ... /* args */) // #func
+{
+    va_list args;
+    vprintf(str, args); // expected-no-warning@#func
+}



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